The delayed time period between the first diagnosis of a head and neck cancer and its treatment can affect not only the clinical staging of the disease, but also its prognosis. The time period for clinical upstaging is studied in a retrospective cohort series. A retrospective case/control series was established to assess the prognosis of head and neck cancer patients due to a delay in treatment. In the first part of the study we included 69 patients who had confirmed clinical upstage before starting the oncologic treatment (cases). The survival of this series was compared to a historical control group of 138 patients matched by tumour site and stage, having received treatment within a short period after their first medical evaluation (controls). We observed that the natural evolution of a head and neck cancer was progressively faster, from an initial clinical stage to an advanced clinical stage until it becomes untreatable. It was observed that the delay in beginning oncologic treatment influenced the prognosis of the patients (P=0.030), especially in clinical stage IV patients (P=0.001) and oral cavity cancer patients (P=0.007).